Enhancing hole-injection efficiency of top-emitting organic light-emitting diodes based on Al/MoNx anodes

High reflectivity bottom anodes are essential for high luminance efficiency top-emitting organic light-emitting diodes (TOLEDs). Although the element Al has high optical reflectivity, its poor hole-injection property severely hinders the realization of high efficient TOLED due to its low work function. In this letter, a high work function MoNx layer with different growth time was deposited on Al layers for enhancing the hole-injection efficiency of TOLEDs. Compared with the bottom-emitting OLED (BOLED) using indium-tin oxide (ITO) anode, the TOLED with Al/MoNx (8 s) anode shows a lower driving voltage of 3.1 eV than that (3.4 eV) of the BOLED at 20 mA/cm2, which may attribute to higher work function of MoNx leading to a stronger hole-injection. Moreover, the TOLED with Al/MoNx (8 s) anode exhibits higher brightness (11800 cd/m2) at 20 mA/cm2, higher maximum current efficiency (64.6 cd/A) and narrower electroluminescence spectra. These results indicate that the Al/MoNx layers could be effective hole-injection anodes for achieving high-performance TOLEDs.